Blow molding machine

ABSTRACT

A construction for neck forming in a blow molding machine of the type having a retractable blow pin at a station separate from the parison extruding station. The construction results in a clean, non-fuzzy neck edge requiring no subsequent cleaning operation, and facilitating stripping of the product from the blow pin. The machine comprises a floating hardened shear ring as part of the blow pin assembly which has an interference fit with flared hardened inserts on the neck portion of the mold halves, thus creating a sharply defined upper neck edge. Means are provided for momentarily releasing downward pressure on the blow pin assembly as the mold halves are being retracted to prevent damage to the inserts. The blow pin assembly incorporates a self-centering arrangement for this shear ring and a controlled compressed air leakage system which cools and spreads the hot flash in the vicinity of the blow pin.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to blow molding machines of the type in whichtubular parison of plastic material is continually extruded at onestation, mold halves for a necked product such as bottle closing aroundthe parison which is severed from the extruder and carried by the moldhalves to a blow molding station. At this station a blow pin assembly islowered against the mold halves to form the neck portion of the productand force compressed air into the parison. The invention is particularlyconcerned with formation of the neck edge and control of the hot flashthereabove.

2. Description of the Prior Art

U.S. Pat. No. 3,470,582 shows a construction for compacting and trimmingnecks in blow molded containers. In this construction, the blow pin hasa shoulder which enters a cylindrical surface on the mold sections.Inevitably, a slight clearance must exist between this blow pin andsurface resulting in a burred or fuzzy neck edge. This must eventuallybe trimmed and reamed at a separate station, often resulting in theinadvertent deposit of resin particles in the bottle.

BRIEF SUMMARY OF THE INVENTION

It is the object of the present invention to provide a novel andimproved blow molding machine in which the neck compacting and trimmingstructure trims the bottle neck in a clean fashion at the moldingstation without the necessity of providing transportion to a separatetrimming machine and eliminating the separate trimming operation.

It is a further object to provide an improved blow molding machine ofthis nature which greatly reduces the cost of construction and operationby not only eliminating the need for transfer equipment and a separatetrimming station but as a result reducing the required floor space.

It is another object to provide an improved blow molding machine neckforming construction of the above nature which minimizes the likelihoodof damage to the equipment and particularly the mold sections when theformed product is released, while at the same time insuring consistentpart size in successive molded products.

It is still another object to provide a novel and improved blow moldingmachine having means for preventing the hot flash in the neck area frominterfering with stripping of the part, while at the same time enhancingthe cooling of the product and portions of the neck forming assembly.

Briefly, the invention in one form comprises a blow molding machine fora product such as a bottle having a neck, comprising a pair of moldsections which together form a cavity and at their upper ends an annularblow pin receiving surface, said surface being flared outwardly in thedirection of the blow pin assembly, and a blow pin assembly having alower portion adapted to fit within said mold cavity so as to form theinside surface of the product neck, a wider portion on said blow pinassembly above said lower portion, and a sharp shoulder between saidportions, the diameter of said shoulder being such that when said blowpin assembly enters said flared surface the outer edge of said shoulderwill engage said flared surface with an interference fit, therebycompletely severing the neck portion of the product from the flashthereabove.

In another aspect, the neck forming system of this invention comprises ablow molding machine blow pin assembly having a blow pin with a centralair passage leading to the mold cavity, an adapter to which said blowpin is secured, said adapter being mounted on a blow pin assemblyactuator, a shear ring carried by said blow pin, said shear ringsurrounding the blow pin and having limited lateral movement withrespect thereto, mold sections forming a surface which surround saidblow pin, said surface being flared in the direction of said adapter,and a shoulder on said shear ring having an interference fit with anintermediate portion of said flared surface. The adapter and blow pinhave facing shoulders between which said shear ring is disposed, thedimensions of the parts being such that clearance for compressed airleakage is present between the shoulder on said blow pin and said shearring, whereby compressed air may leak therethrough and upwardly throughan annular space which is present between the blow pin and shear ring,and air passages in said adapter leading said leaked compressed airradially outwardly, whereby the compressed air will impinge on hot flashlocated inside said flared surface above said interference fit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the fluid controls for the blow pinassembly actuator as well as the coaction with the mold sections;

FIG. 2 is an enlarged fragmentary view partially in cross sectionshowing the construction of the blow pin assembly and its coaction withthe flared mold section surface as well as the neck portion of theproduct; and

FIG. 3 is a cross-sectional enlargement of a portion of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows portions of a continuous extrusion type of blow moldingmachine having an extruder 11 leading to a die head 12 from which iscontinuously extruded a tubular parison 13 of expandable plasticmaterial. A pair of mold sections 14, 15 are mounted for reciprocatingmovement toward and away from each other on opposite sides of parison 13and are also supported for reciprocating movement in unison into and outof the paper of FIG. 1, that is, between the parison extruding stationand a blow molding station at which a blow pin assembly generallyindicated at 16 is present. Conventionally, the mold sections 14, 15close around the extruded parison which is then severed from die head12, the closed mold sections carrying the parison to the blow moldingstation at which point blow pin assembly 16 descends and permitscompressed air to force the parison against the mold cavity 17 formed bysections 14, 15. The present invention is particularly concerned with amold cavity for a product such as a bottle 18 having a neck portiongenerally indicated at 19. In such cases, the mold sectionsconventionally are provided with hardened inserts 21, 22 for cooperationwith the blow pin assembly. As shown in the aforementioned patent, theblow pin assembly is intended not only to permit compressed air to bedelivered to the parison but also to compact the plastic material in thevicinity of portion 19 so as to form the neck including conventional capthreads 23 thereon.

A reciprocating fluid motor 24 is used to move blow pin assembly 16 upand down between its retracted and extended positions. This is in theform of a double acting fluid motor having an upper chamber 25 and lowerchamber 26. The piston rod 27 is hollow in order to carry compressed airfrom a line 28 to the blow pin assembly which is secured to the lowerend of the piston rod. A three-way valve 29 is placed in line 28 and isshiftable by a solenoid 31. When the solenoid is deenergized a spring 32will hold valve 29 in its exhaust position as shown, whereasenergization of solenoid 31 will move the valve to its supply positionin which air from a supply line 33 will be connected to the blow pinassembly.

Fluid to chambers 25 and 26 is controlled by valves 34 and 35. A sourceof fluid pressure 36 is connected to valve 35 which in turn is connectedto valve 34 by a line 37. One outlet port of valve 34 is connected tothe lower chamber 26 by a line 38, and the other port is connected tothe upper chamber 25 by a line 39. Valves 34 and 35 are controlled bysolenoids 41 and 42 respectively and are urged toward their normalpositions when the solenoids are deenergized by springs 43 and 44respectively. When in those positions, as shown in FIG. 1, chamber 26will be compressed and chamber 25 exhausted so that the blow pinassembly is retracted.

FIGS. 2 and 3 show the construction of blow pin assembly 16. Theassembly is secured to the lower end of piston rod 27 by an adapter 45which has a threaded portion 46 mounted in the piston rod. A spacer 47is disposed between the upper end of the adapter and the lower end ofthe piston rod. The blow pin 48 itself has a lower end with radial ports49 and axial port 50, a threaded upper end 51 mounted within adapter 45,and a cylindrical central portion 52, with an upwardly facing shoulder53 between portions 48 and 52.

A shear ring 54 is disposed between the shoulder 55 formed by theunderside of adapter 45 and shoulder 53 of the blow pin. The upperportion of shear ring 54 is cylindrical, with a sharp lower corner 56.The lower portion of the shear ring is somewhat narrower than the upperportion so as to fit within neck portion 19 of the bottle.

The internal diameter 57 of shear ring 54 is somewhat wider than thediameter of blow pin portion 52. Moreover, a slight clearance existsbetween shoulders 53 and 55 and shear ring 54, so that the shear ringmay shift laterally a limited distance. The shear ring will thus have aself-centering action when the blow pin assembly descends.

Inserts 21 and 22 together form a circular recess 58. This recess isflared in an upward direction, and the diameter is such that shoulder 56of shear ring 54 will have an interference fit with the lower portion ofrecess 58. This will mean that the upper edge of bottle neck portion 19will be cleanly finished with the hot flash 59 thereabove being severedfrom the bottle neck.

Means are provided for controlled leakage of compressed air from cavity17 through the blow pin assembly. This means comprises the abovementioned clearance between shear ring 54 and shoulders 53 and 55, plusthe annular space 61 between the shear ring and the main portion of blowpin 48. Compressed air leaking upwardly as shown by the arrows throughthese passages will lead radially outwardly by a plurality of L-shapedpassages 62 formed in adapter 45. This flow of air will serve thepurpose of cooling the hot flash 59 and forcing it away from the blowpin assembly, thus preventing it from sticking to this assembly andfacilitating stripping of the bottle away from the blow pin assembly.The flow of air will also accomplish an air exchange within the bottle,serving to cool the product, and will also cool the floating hardenedshear ring 54 as it passes upwardly through passage 61.

In operation of the system shown in FIGS. 1 and 2, assuming an initialcondition in which mold sections 14, 15 have closed around an extrudedparison 13 and have advanced to the blow molding station, a limit switch63 will be actuated to energize solenoid 41 and shift valve 34, thuscausing chamber 25 of fluid motor 24 to be pressurized so as to causeblow pin assembly 16 to descend into its FIG. 2 position. Solenoid 31will also be energized to shift valve 29 to a position applying blowpressure to the blow pin assembly, thus expanding the parison againstthe mold cavity. The product will be formed, including the neck portion19 which will be compacted and trimmed by the above described action inwhich edge 56 of self-centering shear ring 54 engages tapered surface 58of inserts 21 and 22 with an interference fit.

During this pressurization phase of the cycle, some compressed air willleak through the blow pin assembly at a controlled rate along the pathdescribed above, including passages 61 and 62. This bleed off air systemwill accomplish the purposes of cooling and spreading outwardly the hotflash 59 as well as enhancing cooling of the product by air exchange,and also cooling the hardened shear ring 54.

Upon receipt of a signal solenoid 31 will be deenergized to exhaust thecompressed air from the product and then open the mold sections. Thesignal may be for example from a sensor such as an electric eye 64 whichis at the parison extrusion station and detects the arrival of thebottom of the extruded parison at a certain position, preparatory to thenext pick-up by the mold sections. This signal may simultaneouslyenergize solenoid 42, shifting valve 35 and thus exhausting pressurizedfluid from upper chamber 25 of fluid motor 24. It should be noted thatsolenoid 41 will remain energized at this time so that both chambers 25and 26 will be exhausted. Thus, no downward pressure will be exerted onblow pin assembly 16 as mold sections 14, 15 are opened. Were downwardpressure to be maintained at this time, there would be the danger ofdamage caused to the mold section inserts 21 and 22. This is because, asthe molds begin to open, surface 58 would increase its diameter in onedirection but not in a transverse direction, and the interference fitwith shear ring edge 56 could then cause damage to the insert corners.The above described arrangement for preventing unwanted descent of theblow pin assembly is believed superior to a mechanical stop which wouldinevitably be subject to some yielding movement.

Opening of mold sections 14, 15 will leave finished product 18 hangingon blow pin assembly 16 by friction. When the mold sections reach theiropen positions, a limit switch 65 will be actuated. This will causesolenoid 42 to be deenergized, reapplying pressure to fluid motorchamber 25, it being safe to do so at this time because the moldsections have been completely retracted. The mold sections will bereturned to the parison station to pick up the next parison, and willclose on the new parison. Trimming and transfer means shown in dot-dashlines at 66 in FIG. 1 are attached to and movable with mold sections 14,15, and as the mold sections close upon the new parison, this means 66will close upon the formed product 18 for trimming and transportpurposes. Although this means 66 in itself does not form part of thepresent invention, it is described in order to complete the descriptionof the cycle. A limit switch 67 will sense closure of means 66 on theformed product and thereupon deenergize solenoid 41 to pressurize lowerchamber 26 and exhaust chamber 25 of the fluid motor. This will retractblow pin assembly 16 upwardly.

While it will be apparent that the preferred embodiment of the inventiondisclosed is well calculated to fulfill the objects above stated, itwill be appreciated that the invention is susceptible to modification,variation and change without departing from the proper scope or fairmeaning of the subjoined claims.

I claim:
 1. A blow molding machine for a product such as a bottle havinga neck, comprising a pair of mold sections which together form a cavityand at their upper ends an annular blow pin assembly receiving surface,said surface being flared upwardly in the direction of the blow pinassembly, and a downwardly extending blow pin assembly above said moldsections having actuating means for moving it downwardly to enter saidflared surface and a lower portion adapted to fit within said moldcavity so as to form the inside surface of the product neck, a widerportion on said blow pin assembly above said lower portion, and a sharpshoulder between said portions, the diameter of said shoulder being suchthat when said blow pin assembly enters said flared surface the outeredge of said shoulder will engage said flared surface with aninterference fit, thereby completely severing the neck portion of theproduct from the flash thereabove, said blow pin assembly furthercomprising a blow pin having a central compressed air passage, and ashear ring mounted on said blow pin for limited lateral movement, theinternal diameter of said shear ring being sufficiently wider than theblow pin diameter to permit the shear ring to have a self-centeringaction when the blow pin assembly descends, means longitudinallyretaining said shear ring on said blow pin so as to permit saidself-centering action, said shoulder being formed on said shear ring. 2.The combination according to claim 1, said blow pin assembly furthercomprising an adapter member, said blow pin being attached to saidadapter member, an actuator for said blow pin, said adapter member beingsecured to one end of said actuator, said shear ring being disposedbetween facing shoulders on said adapter and blow pin.
 3. Thecombination according to claim 2, further provided with sufficientclearance between the shear ring and said blow pin to permit leakage ofcompressed air from the interior of the product being molded past saidshear ring, and air passages in said adapter leading said compressed airradially outwardly against the hot flash surrounding said blow pinassembly above said shear ring shoulder.
 4. The combination according toclaim 2, said shear ring shoulder being at an intermediate portionthereof, the portion of said shear ring below said shoulder being formedso as to coact with material on the inside of the product neck.
 5. Ablow molding machine comprising a pair of mold sections forming a moldcavity, a blow pin assembly above said mold sections having a blow pinwith a central air passage leading downwardly to the mold cavity, anadapter to which said blow pin is secured, said adapter being mounted ona blow pin assembly actuator, a shear ring carried by said blow pin,said shear ring surrounding the blow pin and having limited lateralmovement with respect thereto, the internal diamater of said shear ringbeing sufficiently wider than the blow pin diameter to permit the shearring to have a self-centering action when the blow pin assemblydescends, means longitudinally retaining said shear ring on said blowpin so as to permit said self-centering action, said mold sectionsforming a surface which surrounds said blow pin when the mold and blowpin assembly are engaged, said surface being flared upwardly in thedirection of said adapter, and a shoulder on said shear ring having aninterference fit with an intermediate portion of said flared surfacewhen the mold and assembly are engaged.
 6. The combination according toclaim 5, the adapter and blow pin having facing shoulders between whichsaid shear ring is disposed, the dimensions of the parts being such thatclearance for compressed air leakage is present between the shoulder onsaid blow pin and said shear ring, whereby compressed air may leaktherethrough and upwardly through an annular space which is presentbetween the blow pin and shear ring.
 7. The combination according toclaim 6, further provided with air passages in said adapter leading saidleaked compressed air radially outwardly, whereby the compressed airwill impinge on hot flash located inside said flared surface above saidinterference fit.